Light polarizing film

ABSTRACT

A light polarizing film and method of making same includes a linear polarizer having a first surface and a second surface and having a polarization direction, an optical retarder comprising a simultaneously biaxially oriented polypropylene film disposed adjacent to the first surface of the linear polarizer and having an axis oriented at an angle with respect to the polarization direction, and an adhesive layer disposed between the first surface of the linear polarizer and the optical retarder and having a minimum adhesion strength of about 25 grams per inch.

CROSS REFERENCE TO RELATED APPLICATION INFORMATION

This application is a divisional of U.S. Ser. No. 10/365,333 filed Feb.12, 2003, now allowed, the disclosure of which is herein incorporated byreference.

FIELD OF THE INVENTION

This invention relates to a light polarizing film including a linearpolarizer and an optical retarder and, in particular, a polarizing filmincluding a synthetic dichroic linear polarizer and an optical retarderin the form of a simultaneously biaxially oriented polymer film.

BACKGROUND OF THE INVENTION

Unpolarized light waves vibrate in a large number of planes about theaxis of a light beam. If the light waves vibrate in one plane only, thelight is said to be plane polarized. While several materials possess toa degree inherent polarizing properties, synthetic polarizing materialsbased on thin polymeric films are desirable for their comparative easeof manufacture and handling, their ability to be tailored for particularuses, and the comparative ease with which they may be incorporated intodesired end products.

The production of linear light polarizing films has been well describedin the art. Linear light polarizing films, in general, owe theirproperties of selectively passing radiation vibrating along a givenelectromagnetic radiation vector and absorbing electromagnetic radiationvibrating along a second given electromagnetic radiation vector to theanisotropic character of the transmitting film medium.

Dichroic polarizers are an absorptive variety of linear polarizers thatowe their light-polarizing capabilities to the vectorial anisotropy oftheir absorption of incident light waves. The term “dichroism” is usedherein to refer to the property of differential absorption of thecomponents of an incident beam of light, depending upon the vibrationdirections of the components. Thus, light entering a dichroic filmencounters two different absorption coefficients acting on light wavesvibrating along different planes, one coefficient being low and onecoefficient being relatively high. The emerging light vibratespredominantly in the direction of low absorption. One type of syntheticdichroic sheet polarizer is a polyvinyl alcohol-iodine complex polarizerand variants thereof, such as an “H-Sheet”-type polarizer or stainedpolarizer, the first such polarizer having been invented by Edwin H.Land of Polaroid Corporation and described in U.S. Pat. No. 2,454,515.In general, a polyvinyl alcohol-iodine complex polarizer comprises alight-absorptive linear polyiodide contained within a polyvinyl alcoholmatrix. A polyvinyl alcohol-iodine complex polarizer is generally made,for example, by impregnating a film of polyvinyl alcohol or itsderivative with an aqueous solution of a light-absorptive polyiodide orsimilar dichroic dye, and thermally stretching the film several timesits length so that the resultant high molecular weight molecules areunidirectionally oriented. By orienting the polyvinyl alcohol matrixunidirectionally, the transition moments of the light-absorptivepolyiodide become correspondingly oriented, and the material thusbecomes visibly dichroic.

Another type of synthetic dichroic sheet polarizer is an intrinsicpolarizer, such as a K-type polarizer. An intrinsic polarizer derivesits dichroism from the light-absorbing properties of its matrix, notfrom the light-absorbing properties of dye additives, stains, orsuspended crystalline material. Typically intrinsic polarizers comprisea sheet of oriented poly(vinyl alcohol) having an oriented suspension ofa dehydration product of polyvinyl alcohol (i.e., polyvinylene).Intrinsic polarizers of this kind are formed by heating the polymericsheet in the presence of a dehydration catalyst, such as vapors ofaqueous hydrochloric acid, to produce conjugated polyvinylene blocks andunidirectionally stretching the polymeric sheet prior to, subsequent to,or during the dehydration step to align the poly(vinyl alcohol) matrix.By orienting the poly(vinyl alcohol) matrix unidirectionally, thetransition moments of the conjugated polyvinylene blocks or chromophoresare also oriented, and the material becomes visibly dichroic. A secondorientation step or extension step may be employed after the dehydrationstep, as described in U.S. Pat. No. 5,666,223 (Bennett et al.).

An optical retarder modifies polarized light by retarding the opticalpath length for one of the orthogonal components of the light comparedto the other orthogonal component. When the light emerges from theoptical or phase retarder, there is a phase difference between the twoorthogonal components of linearly polarized light. A circular polarizeror elliptical polarizer may be produced when an optical retarder is usedin combination with a linear polarizer. Circularly polarized light iscreated when the two orthogonal components of linearly polarized lightare phase shifted with respect to each other by λ/4, where λ representsthe wavelength of the light. Elliptically polarized light results froman arbitrary phase shift between the two orthogonal components ofincoming light. For example, a ray of unpolarized light passing througha linear polarizer becomes polarized in the polarization direction ofthe linear polarizer. When the polarization direction of the light isoriented 45 degrees with respect to the optical axis of the retarder,the resulting light is circularly or elliptically polarized, and thevibration direction of the polarized light ray after passing through theretarder appears to move in a helical pattern.

SUMMARY OF THE INVENTION

In general, in one aspect, the invention features a light polarizingfilm. The light polarizing film includes a linear polarizer having afirst surface and a second surface and having a polarization direction,and an optical retarder including a simultaneously biaxially orientedpolypropylene film disposed adjacent to the first surface of the linearpolarizer and having an axis oriented at an angle to the polarizationdirection.

In general, in another aspect, the invention features a method forproducing a light polarizing film. An oriented sheet of polyvinylalcohol having a first surface and a second surface and having apolarization direction is provided. An optical retarder including asimultaneously biaxially oriented polypropylene film is disposedadjacent to the first surface of the linear polarizer. An axis of theoptical retarder is oriented at an angle to the polarization directionof the linear polarizer. The oriented sheet of polyvinyl alcohol istreated with a light absorbing material.

In general, in another aspect, the invention features an optical system,which includes a polarized light source and a light polarizing film. Thelight polarizing film includes a linear polarizer with a first surfaceand a second surface and having a polarization direction, and an opticalretarder including a simultaneously biaxially oriented polypropylenefilm disposed adjacent to the first surface of the linear polarizer andhaving an axis oriented at an angle to the polarization direction.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a light polarizing film according toan embodiment of the present invention;

FIG. 2 is a perspective view of a light polarizing film according to anembodiment of the present invention;

FIG. 3 is a schematic side view of a light polarizing film according toan embodiment of the present invention; and

FIG. 4 is a schematic side view of a light polarizing film according toan embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a schematic side view of a light polarizing film 10according to the present invention. Light polarizing film 10 includes alinear polarizer 12 having a first surface 12 a and a second surface 12b, and an optical retarder 14 comprising a simultaneously biaxiallyoriented polymer film disposed adjacent to the first surface 12 a oflinear polarizer 12. The combination of linear polarizer 12 and opticalretarder 14 is a light polarizing film 10 which functions as anelliptical or circular polarizer. Typically, linear polarizer 12 is inclose proximity to optical retarder 14, although this arrangement is notrequired. Preferably, the two layers 12, 14 are bonded to each other bya layer of adhesive 16.

As shown in FIG. 2, linear polarizer 12 is configured or oriented withinlight polarizing film 10 such that a polarization axis or direction 20of linear polarizer 12 has an absolute angular offset, θ, relative to anoptical axis 22 of optical retarder 14, of from about 1 degree to about90 degrees, preferably about 45 degrees. Polarization direction 20indicates the plane along which linearly polarized light emerges fromlinear polarizer 12. Polarization direction 20 will in most casescorrespond with the stretch direction of the polarizer, i.e., thedirection of polymeric and/or chromophoric orientation.

Light polarizing film 10 may be made with any type of linear polarizer12, but is preferably made with a synthetic dichroic polarizer, such asan intrinsic polarizer or a polyvinyl alcohol-iodine complex polarizerand variants thereof. Typically, when processing an intrinsic polarizeror a polyvinyl alcohol-iodine complex polarizer, the film may bestretched in a machine direction as with a length orienter, across thewidth or transverse to the machine direction using a tenter, and/or at adiagonal to the machine direction. When a polymeric sheet is stretchedin more than one direction, the polarization direction of the resultingpolarizer typically is determined by the direction of the largest degreeof stretch.

Optical retarder 14 is typically made from an orientable polymer film,such as a polypropylene or polyester film, which may be madebirefringent, for example, by stretching the polymer film in a desireddirection or directions. The term “birefringent” means that the indicesof refraction in orthogonal x, y, and z directions are not all the same.For films or layers in a film, a convenient choice of x, y, and z axesis shown in FIG. 2 in which the x and y axes correspond to the lengthand width of the film or layer, respectively, and the z axis correspondsto the thickness of the layer or film. For example as shown in FIG. 2,the machine direction corresponds to the x-axis.

When an orientable polypropylene or polyester film is stretched alongthe x axis, the typical result is that the indices of refraction, n_(x)and n_(y), are not equal for light polarized in a plane parallel to the“x” and “y” axes, respectively. The degree of alteration in the index ofrefraction along the stretch direction will depend on factors such asthe amount of stretching, the stretch rate, the temperature of the filmduring stretching, the thickness of the film, the variation in filmthickness, and the composition of the film.

In making optical retarder 14, a biaxial stretch process is preferablyused to orient the birefringent material in the plane of the film, e.g.,a flat film tenter stretching process. Biaxially stretched as usedherein to describe a film, indicates that the film has been stretched intwo different directions. The biaxial stretching of a film in twodifferent directions may result in a net symmetrical or asymmetricalstretch in the two chosen axes. Typically, but not always, the twodirections are substantially orthogonal and are in the machine directionof the film and the transverse direction of the film. Preferably,optical retarder 14 has its optical axis in the machine direction.Biaxially stretched films may be drawn in the two directionssequentially, simultaneously, or some combination of sequentially andsimultaneously. A simultaneously biaxially oriented film when usedherein indicates that significant portions of the stretching in each ofthe two directions are performed simultaneously. Simultaneouslybiaxially oriented polypropylene is an especially preferred material forforming optical retarder 14 because it is inexpensive, easy tomanufacture, and provides mechanical strength to linear polarizer 12.Examples of simultaneously biaxially oriented films are described inU.S. Pat. Nos. 3,241,662, 3,324,218, 6,303,067 and 6,358,457.

Adhesive layer 16 is typically made from a pressure sensitive adhesive.Pressure sensitive adhesives may be prepared from a compositioncomprising, for example, a major amount of one or more thermoplasticpolymers and may optionally contain such other desired components asUV-absorbers, anti-static compositions, optical brighteners, inertfillers, and plasticizers. Pressure sensitive adhesive should besufficiently compatible with the light polarizer material and theoptical retarder material to substantially prevent degradation of thetwo films. Pressure sensitive adhesive should also have a degree ofoptical transparency and clarity sufficient to substantially preventdepolarization, and other like optical distortions. The adhesion orsticking strength of adhesive layer 16 is typically greater than about25 grams/inch as measured using a peel tester operated at 90 in/min peelrate, 180 degree peel. An example of suitable simultaneously biaxiallyoriented polypropylene films having an accompanying layer of adhesivesuch as a pressure sensitive adhesive are commercially available from 3MCompany (St. Paul, Minn.), for example the product designations 3701Tape and 3750 Tape. 3701 Tape has a thickness of about 0.002 inches(0.051 mm), and 3750 Tape has a thickness of about 0.0035 inches (0.089mm).

To facilitate the mass production of a light polarizing film 10, thepresent invention also provides a method of manufacture wherein linearpolarizer 12 having a polarization direction 20 at a predefined angle,e.g., ±45 degrees relative to the machine direction of linear polarizer12, is roll-to-roll laminated (or otherwise deposited) onto opticalretarder 14 having an optical axis 22 at a predefined angle, e.g.,parallel to the machine direction of optical retarder 14. Lightpolarizing film 10 of the present invention is easier and moreinexpensive to manufacture since a subsequent alignment step of linearpolarizer 12 with optical retarder 14 is not necessary. Since therelative orientation of polarization direction 20 of linear polarizer 12to optical axis 22 of optical retarder 14 is preferably at 45 degrees,linear polarizer 12 is preferably stretched or has a largest degree ofstretch at a 45 degree angle to the machine direction. One method ofstretching a polymeric sheet along a diagonal is described in U.S. Pat.No. 2,505,146, which is hereby incorporated by reference.

One use of light polarizing film 10 involves illuminating opticalretarder 14 with polarized light 18 as illustrated in FIG. 2. Theincoming polarized light 18 is preferably oriented parallel to orperpendicular to polarization direction 20 of linear polarizer 12.Although the present invention will be discussed with reference to thisconfiguration, other configurations in which linear polarizer 12,optical retarder 14, and incoming polarized light 18 are oriented indifferent manners with respect to one other are also possible.

After the incoming polarized light 18 passes through optical retarder14, the light becomes elliptically or circularly polarized. Theretardance of optical retarder 14 determines the amount the phase isshifted between the two orthogonal components of the polarized light,and thus determines whether the light becomes elliptically or circularlypolarized. If the light is elliptically polarized, the eccentricity ofthe ellipse varies with the amount the phase is shifted. Preferably, thephase is shifted 200 nm, or a multiple thereof, to produce a variety ofelliptically and circularly polarized forms throughout the visiblerange. Typically, optical retarder 14 has a retardance ranging fromabout 200 nm to about 3000 nm.

When the elliptically or circularly polarized light passes throughlinear polarizer 12, polarizer 12 absorbs a portion of the lightcomponents that emerged from optical retarder 14. Moreover, sinceoptical retarder 14 will shift the phase of different wavelengths oflight to different extents, polarizer 12 will absorb differentwavelengths selectively, and thus the emerging light will besubstantially colored. For example, if optical retarder 14 has aretardance of about 300 nm, the emerging light may have a blue color ora yellow color, depending on the initial orientation of polarized light18. The color or wavelength of the emerging light may also varydepending on the direction of the viewing angle.

FIG. 3 shows a schematic side view of another embodiment of a lightpolarizing film 10. Light polarizing film 10 includes a linear polarizer12 and an optical retarder 14 as shown and previously described in FIG.1, along with a second optical retarder 24 comprising a simultaneouslybiaxially oriented polymer film disposed adjacent to the second surface12b of linear polarizer 12. Typically, linear polarizer 12 is in closeproximity to second optical retarder 24, although this arrangement isnot required. Preferably, the two layers 12, 24 are bonded to each otherby a layer of adhesive 16. Second optical retarder 24 provides furtherstructural support to light polarizing film 10, but does not change theintensity of the emerging light as described previously with respect tothe optical system shown in FIG. 2. Additionally, second opticalretarder 24 allows polarized light 18 to illuminate either side of lightpolarizing film 10 and still produce a similar optical effect.

FIG. 4 shows a schematic side view of a light polarizing film 10 with alinear polarizer 12 and an optical retarder 14 as shown and previouslydescribed in FIG. 1, along with a second light polarizing film 10 with alinear polarizer 12 and an optical retarder 14. A second opticalretarder 24 may be used on either of the light polarizing films 10.Although FIG. 4 shows a stack 30 of two light polarizing films, anynumber of light polarizing films with various thicknesses and layers maybe used. The use of multiple light polarizing films may be used toproduce varying optical effects.

The polymeric sheet used to make the linear polarizer generally has athickness on the order of 0.0005 inches (0.013 mm) to 0.004 inches(0.102 mm). The polymeric sheet is typically stretched fromapproximately 3.5 times to approximately 6.0 times the original lengthof the sheet. The stretching step is conducted at a temperature abovethe glass transition temperature of the polymeric material. Stretchingmay be effected by the provision of heat generating elements, fastrollers, and slow rollers. For example, the difference in the rotationalrate between rollers may be exploited to create corresponding tension inthe area of the sheet transported therebetween. When heat generatingelements heat the sheet, stretching is facilitated and more desirablyeffected. Temperature control may be achieved by controlling thetemperature of heated rolls or by controlling the addition of radiantenergy, e.g., by infrared lamps, as is known in the art. A combinationof temperature control methods may be utilized.

Due to the relative weak transverse strength of an oriented vinylalcoholpolymer, it may be advantageous to cast, laminate or otherwise affix thevinylalcohol film onto a substrate such as a support film layer, heatedroller, or carrier web after orientation. A support layer, when bondedor otherwise affixed to the polymer film provides mechanical strengthand support to the article so that it may be more easily handled andfurther processed.

In the case of a polyvinyl alcohol-iodine complex polarizer, thepolymeric sheet either before or after being oriented is treated orsubmerged in an iodine solution. In the case of an intrinsic polarizer,the oriented polymeric sheet is subjected to a dehydration stepwhereupon the oriented sheet is treated to “convert” a portion thereofto polarizing molecules consisting of block copolymers ofpoly(vinylene-co-vinyl alcohol). Methods of producing polyvinylalcohol-iodine complex polarizers and intrinsic polarizers are describedin U.S. Pat. No. 4,166,871 (Schuler); U.S. Pat. No. 4,591,512 (Racich etal.); and U.S. Pat. No. 5,666,223 (Bennett et al.).

In the case of an intrinsic polarizer, the polymeric sheet may besubjected to a second orientation step or extension step in which theoriented polarizer is stretched a second time from about 0% to about 70%beyond that obtained in the first stretch. For any type of polarizerfilm, the polymeric sheet may also be subjected to a boration step inwhich the oriented sheet is treated with an aqueous solution of boricacid and borax to effect relaxation and crosslinking. The extension stepmay be carried out before, during or after the polymeric sheet is in aboration solution. For example, the polymeric sheet can be submerged andallowed to soften and/or swell (i.e., relax) in the boration solution,subsequently removed, and then extended. Alternatively, the polymericsheet may be extended when still submerged into the boric acid solution.

The boration step may employ two or more baths. For example, in atwo-bath boration treatment, the first bath may contain water, and thesecond, a boric ion contributing species. Alternatively, the order canbe reversed or both baths may contain varying concentrations and/ormixtures of boric ion contributing species. Extension may be conductedin any one of these baths.

When the polymeric sheet is borated, the boration solution willgenerally comprise boric acid and either sodium or potassium hydroxide,or a substance from the class consisting of the sodium and potassiumborates, preferably borax. The concentration of boric acid and borax orother borate in the solution or solutions to which the orientedpolarizing sheet is subjected are not critical. Preferably, the boricacid is present in a higher concentration than the borax or otherborate, and a preferred concentration range comprises 9%-12% by weightof boric acid and 3% by weight of borax. Preferably, the solutionsshould contain from about 1% to about 7% by weight of borax and fromabout 5% to about 20% by weight of boric acid.

One or more dichroic dyes may additionally be added to the polymericsheet in order to neutralize the so-called “blue-leak” and/or “red-leak”of certain dichroic polarizers. Any of a variety of dichroic dyes may beused. Suitable dyes include any of the diazo, triazo or polyazo dyes, orother direct or acid dyes, such as “Intrajet Yellow DG” available fromSensient Technical Colors (Elmwood Park, N.J.) and “Evans Blue”available from Sigma-Aldrich. The dichroic dye may be added to thepolymeric sheet at any stage in the process. For example, the dye may becast into or coated onto the polymeric sheet before the initial stretch,or it may be added during the dehydration, iodine staining, boration, orextension step. A variety of time, temperatures, and concentrations maybe used depending on the amount of stain required. Higher temperaturesand/or higher concentrations may require less residence time for thepolymeric sheet.

Subsequent to the boration step and/or extension step, the orientedpolymeric film may be subjected to a baking temperature ranging fromabout 50° C. to about 90° C. The resulting polarizer can again be bondedor laminated to a support layer, the support layer being the same ordifferent from the layer stripped off, fumed, iodine stained and/ororiented prior to extension thereof.

Any of a variety of materials can be used for the carrier web or supportlayer. Suitable materials include known polymeric sheet materials suchas the cellulose esters (e.g., nitrocellulose, cellulose acetate,cellulose acetate butyrate), polyesters, polycarbonates, vinyl polymerssuch as the acrylics, and other support materials that can be providedin a sheet-like, light-transmissive form. Polyesters are especiallyuseful, depending on the particular application and the requirementsthereof. A preferred polyester is polyethylene terephthalate, availableunder the Mylar and Estar tradenames, although other polyethyleneterephthalate materials can be employed. The thickness of the supportmaterial will vary with the particular application. In general, from thestandpoint of manufacturing considerations, supports having a thicknessof about 0.0005 inches (0.013 mm) to about 0.020 inches (0.508 mm) canbe conveniently employed.

During the processing of the polymeric film, optical retarder 14 may bebonded to the oriented polymeric film before or after the iodinestaining, in the case of a polyvinyl alcohol-iodine complex polarizer,and before or after the dehydration in the case of an intrinsicpolarizer. Optical retarder 14 may then be subjected to a boration,extension, and/or heat treatment step. Alternatively, optical retarder14 may be bonded or laminated onto the dichroic polarizer after allprocessing steps are completed for making the polarizer.

It will be apparent to those of ordinary skill in the art that lightpolarizing films of the present invention may be laminated between or tosupporting sheets or films, such as sheets of glass or sheets of otherorganic plastic materials, and that light polarizing films of thepresent invention in either laminated or unlaminated form may beemployed wherever other forms of light-polarizing plastic materials maybe used, for example, in connection with liquid crystal display panels,or other display devices.

Any of a variety of adhesives can be used for laminating the lightpolarizing films onto other layers or substrates including polyvinylalcohol adhesives and polyurethane adhesive materials. Since the lightpolarizing films are normally employed in optical applications, anadhesive material which does not have an unacceptable effect on thelight transmission properties of the light polarizing film willgenerally be employed. The thickness of the adhesive material will varywith the particular application. In general, thicknesses of about 0.0002inches (0.005 mm) to about 0.002 inches (0.051 mm) are satisfactory.

Various functional layers or coatings may be added to the lightpolarizing film of the present invention to alter or improve itsphysical or chemical properties, particularly along the surface of thefilm. Such layers or coatings may include, for example, slip agents, lowadhesion backside materials, conductive layers, antistatic coatings orfilms, barrier layers, flame retardants, UV stabilizers, abrasionresistant materials, optical coatings, compensation films, diffuselayers, diffuse adhesives, and/or substrates designed to improve themechanical integrity or strength of the film.

Skin layers or coatings may also be added to impart desired barrierproperties to the resulting film or device. Thus, for example, barrierfilms or coatings may be added as skin layers, or as a component in skinlayers, to alter the transmissive properties of the film towardsliquids, such as water or organic solvents, or gases, such as oxygen orcarbon dioxide.

Skin layers or coatings may also be added to impart or improve abrasionresistance in the resulting article. Thus, for example, a skin layercomprising particles of silica embedded in a polymer matrix may be addedto an optical film produced in accordance with the invention to impartabrasion resistance to the film, provided, of course, that such a layerdoes not unduly compromise the optical properties required for theapplication to which the film is directed.

Skin layers or coatings may also be added to impart or improve punctureand/or tear resistance in the resulting film. Factors to be consideredin selecting a material for a tear resistant layer include percentelongation to break, Young's modulus, tear strength, adhesion tointerior layers, percent transmittance and absorbance in anelectromagnetic bandwidth of interest, optical clarity or haze,refractive indices as a function of frequency, texture and roughness,melt thermal stability, molecular weight distribution, melt rheology andcoextrudability, miscibility and rate of inter-diffusion betweenmaterials in the skin layer and polarizing film layers, viscoelasticresponse, relaxation and crystallization behavior under draw conditions,thermal stability at use temperatures, weatherability, ability to adhereto coatings and permeability to various gases and solvents.

Puncture or tear resistant skin layers may be applied during themanufacturing process or later coated onto or laminated to thepolarizing film. Adhering these layers to the film during themanufacturing process, such as by a coextrusion process, provides theadvantage that the film is protected during the manufacturing process.In some embodiments, one or more puncture or tear resistant layers maybe provided within the film, either alone or in combination with apuncture or tear resistant skin layer.

The light polarizing film of the present invention may be given goodslip properties by treating it with low friction coatings or slipagents, such as polymer beads coated onto the surface. Alternately, themorphology of the surfaces of these materials may be modified, asthrough manipulation of extrusion conditions, to impart a slipperysurface to the films.

In some applications, it may be desirable to treat the light polarizingfilm, optical retarder, or linear polarizer with low adhesion backsize(LAB) coatings or films such as those based on urethane, silicone orfluorocarbon chemistry. Films treated in this manner will exhibit properrelease properties towards pressure sensitive adhesives, therebyenabling them to be treated with adhesive and wound into rolls.

The light polarizing film of the present invention may also be providedwith one or more conductive layers. Such conductive layers may includemetals such as silver, gold, copper, aluminum, chromium, nickel, tin,and titanium, metal alloys such as silver alloys, stainless steel, andinconel, and semiconductor metal oxides such as doped and undoped tinoxides, zinc oxide, and indium tin oxide.

The light polarizing film of the present invention may also be providedwith antistatic coatings or films. Such coatings or films include, forexample, V₂O₅ and salts of sulfonic acid polymers, carbon or otherconductive metal layers.

The light polarizing film of the present invention may also be providedwith abrasion-resistant or hard coatings, which may be applied as a skinlayer. These include acrylic hardcoats such as Acryloid A-11 andParaloid K-120N, available from Rohm & Haas, Philadelphia, Pa.; urethaneacrylates, such as those described in U.S. Pat. No. 4,249,011 and thoseavailable from Sartomer Corp., Westchester, Pa.; and urethane hardcoatsobtained from the reaction of an aliphatic polyisocyanate (e.g.,Desmodur N-3300, available from Miles, Inc., Pittsburgh, Pa.) with apolyester (e.g., Tone Polyol 0305, available from Union Carbide,Houston, Tex.).

One or more of the non-optical layers previously mentioned may be formedas a skin layer over at least one surface of light polarizing film 10 orlight polarizing stack 30, for example, to protect linear polarizer 12from physical damage during processing and/or afterwards. In addition,one or more of non-optical layers may be formed within light polarizingfilm 10 or light polarizing stack 30, for example, to provide greatermechanical strength or to protect the film or stack during processing.

The non-optical layers, such as adhesive layer 16, ideally do notsignificantly participate in the determination of optical properties oflight polarizing film 10, at least across the wavelength region ofinterest, the visible spectrum. The non-optical layers are typically notbirefringent or orientable, although this is not required. Typically,when the non-optical layers are used as skin layers there may be somesurface reflection. When the non-optical layers are found within lightpolarizing film 10, there will typically be at least some polarizationor reflection of light by the non-optical layers in combination with theoptical layers 12, 14, and 24 adjacent to the non-optical layers.

The light polarizing film of the present invention may further belaminated to rigid or semi-rigid substrates, such as, for example,glass, metal, acrylic, polyester, and other polymer backings to providestructural rigidity, weatherability, or easier handling. For example,the polarizing film 10 may be laminated to a thin acrylic or metalbacking so that it can be stamped or otherwise formed and maintained ina desired shape. For some applications, such as when the film is appliedto other breakable backings, an additional layer comprising asimultaneously biaxially oriented polymer film or puncture-tearresistant film may be used.

Various optical layers, materials, and devices may also be applied to,or used in conjunction with, the light polarizing film of the presentinvention for specific applications. These include, but are not limitedto, magnetic or magneto-optic coatings or films; liquid crystal panels,such as those used in display panels and privacy windows; photographicemulsions; fabrics; prismatic films, such as linear Fresnel lenses;brightness enhancement films; holographic films or images; embossablefilms; anti-tamper films or coatings; IR transparent films for lowemissivity applications; release films or release coated paper;compensation films; diffuse adhesives; and polarizers or mirrors.

The light polarizing film made in accordance with the invention may alsoinclude one or more anti-reflective layers or coatings, such as, forexample, conventional vacuum coated dielectric metal oxide ormetal/metal oxide optical films, silica sol gel coatings, and coated orcoextruded anti-reflective layers such as those derived from low indexfluoropolymers such as THV, an extrudable fluoropolymer available from3M Company (St. Paul, Minn.). Such layers or coatings, which may or maynot be polarization sensitive, serve to increase transmission and toreduce reflective glare, and may be imparted to the films and opticaldevices of the present invention through appropriate surface treatment,such as coating or sputter etching.

Multiple additional layers on one or both surfaces of light polarizingfilm 10, linear polarizer 12, and optical retarder 14 are contemplated,and may be in any combination of the aforementioned coatings or films.

The light polarizing film of the present invention may be treated withinks, dyes, or pigments to alter its appearance or to customize it forspecific applications. Various types of ink can be used, including oneand two component inks, oxidatively drying and UV-drying inks, dissolvedinks, dispersed inks, and 100% ink systems. In addition, a dye orpigment may be blended in with a polymer during any portion of theprocessing.

The appearance of the light polarizing film may also be altered bycoloring the film, such as by laminating a dyed film to the polarizingfilm, applying a pigmented coating to the surface of the film, orincluding a pigment in one or more of the materials used to make thefilm.

Both visible and near IR dyes and pigments are contemplated in thepresent invention, and include, for example, optical brighteners such asdyes that absorb in the UV and fluoresce in the visible region of thecolor spectrum. Other additional layers that may be added to alter theappearance of the polarizing film include, for example, opacifying(black) layers, diffusing layers, holographic images or holographicdiffusers, and metal layers. Each of these may be applied directly toone or both surfaces of film, or may be a component of a second film orfoil construction that is laminated to the film. Alternately, somecomponents such as diffusing agents, or colored pigments, may beincluded in an adhesive layer which is used to laminate the film toanother surface.

Various modifications and alterations of this invention will be apparentto those skilled in the art without departing from the scope and spiritof this invention.

1. A light polarizing film comprising: a linear polarizer having a firstsurface and a second surface and having a polarization direction whereinthe polarization direction is about 45 degrees relative to a machinedirection of the linear polarizer; an optical retarder comprising asimultaneously biaxially oriented polypropylene film disposed adjacentto the first surface of the linear polarizer and having an axis orientedat an angle with respect to the polarization direction; and an adhesivelayer disposed between the first surface of the linear polarizer and theoptical retarder and having a minimum adhesion strength of about 25grams per inch.
 2. The polarizing film of claim 1 wherein the retardanceof the optical retarder ranges from about 200 nm to about 3000 nm. 3.The polarizing film of claim 1 further comprising a second opticalretarder comprising a biaxially oriented polypropylene film disposedadjacent to the second surface of the linear polarizer.
 4. Thepolarizing film of claim 3 further comprising an adhesive layer disposedbetween the second surface of the linear polarizer and the secondoptical retarder and having a minimum adhesion strength of about 25grams per inch.
 5. The polarizing film of claim 1 wherein the angle isabout 45 degrees.
 6. The polarizing film of claim 1 wherein the linearpolarizer is a synthetic dichroic polarizer.
 7. The polarizing film ofclaim 6 wherein the synthetic dichroic polarizer is a polyvinylalcohol-iodine complex polarizer or an intrinsic polarizer.
 8. Thepolarizing film of claim 1 wherein the polarization direction is about45 degrees relative to a machine direction of the linear polarizer.
 9. Alight polarizing film comprising: a linear polarizer having a firstsurface and a second surface and having a polarization direction whereinthe polarization direction is about 45 degrees relative to a machinedirection of the linear polarizer; an optical retarder comprising asimultaneously biaxially oriented polymer film disposed adjacent to thefirst surface of the linear polarizer and having an axis oriented at anangle to the polarization direction; and an adhesive layer disposedbetween the first surface of the linear polarizer and the opticalretarder and having a minimum adhesion strength of about 25 grams perinch.
 10. The polarizing film of claim 9 wherein the simultaneouslybiaxially oriented polymer film comprises polyester.